Fix markdown lint error

Author: mfussenegger

README.md

@@ -505,7 +505,7 @@ If you get an error like:
 
 ```text
 E5113: Error while calling lua chunk: ...uarocks/lib/luarocks/rocks-5.1/busted/2.2.0-1/bin/busted:3: module 'busted.runner' not found:
-	no field package.preload['busted.runner']
+    no field package.preload['busted.runner']
 ```
 
 You need to run `eval $(luarocks path --no-bin)` first.